Photo- and Thermal-Induced Multistructural Transformation of 2-Phenylazolyl Chelate Boron Compounds

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• 作者：Ying-Li Rao ; Hazem Amarne ; Leanne D. Chen ; Matthew L. Brown ; Nicholas J. Mosey ; Suning Wang
• 刊名：The Journal of the American Chemical Society
• 出版年：2013
• 出版时间：March 6, 2013
• 年：2013
• 卷：135
• 期：9
• 页码：3407-3410
• 全文大小：286K
• 年卷期：v.135,no.9(March 6, 2013)
• ISSN：1520-5126

文摘

The new N,C-chelate boron compounds B(2-phenylazolyl)Mes₂ [Mes = mesityl; azolyl = benzothiazolyl (1a), 4-methylthiazolyl (2a), benzoxazolyl (3a), benzimidazolyl (4a)] undergo an unprecedented multistructural transformation upon light irradiation or heating, sequentially producing isomers b, c, d, and e. The dark isomers b generated by photoisomerization of a undergo a rare thermal intramolecular H-atom transfer (HAT), reducing the azole ring and generating new isomers c, which are further transformed into isomers d. Remarkably, isomers d can be converted to their diastereomers e quantitatively by heating, and e can be converted back to d by irradiation at 300 nm. The structures of isomers 1d and 1e were established by X-ray diffraction. The unusual HAT reactivity can be attributed to the geometry of the highly energetic isomers b and the relatively low aromaticity of the azole rings. The boryl unit plays a key role in the reversible interconversion of d and e, as shown by mechanistic pathways established through DFT and TD-DFT calculations.